I have my own smart contract that has the transfer function in it. I want to write some javascript function that can only be called from my other application that will automatically approve and send the tokens to a wallet. I want this to happen without any manual approval for each transaction by me as the owner of the smart contract. How can this be done?
Thanks in advance.
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Say, I have an interactive dapp, like a game and I want the user's actions to be saved on the blockchain (maybe these are moves in the game of chess, whatever).
So, from my understanding, options are:
Create dynamic wallet via web3, prefill it from the metamask and send as many transactions as I want.
Somehow negotiate with the user to trust the dapp and let metamask send transactions on user's behalf without pesky prompting.
What is the right option (if any)? Turns out, metamask has a whole permission escalation framework, yet I wasnt able to ask the right permission.
You can access user funds in several ways:
ask users to deposit in a smart contract and keep track of balances there
ask users to allow your smart contract to spend their tokens via ERC20 allowance
How often will user actions be saved on the blockchain?
Even if your dapp has access to all user funds via a shared wallet or ERC20 allow() + transferFrom() you'll still need somebody to trigger a transaction and pay gas fees whenever you're updating chain state.
I'm just getting started with Watson Dialog service and I'm trying to ensure that I don't allow my users to attempt to resume a conversation with the bot if their conversation session is no longer valid. Is there an expiration on Dialog conversations at all? Or does IBM simply store conversations forever?
EDIT:
If there is a method to determine whether a Dialog Conversation has expired, please provide a link to documentation, or an example, of said method.
If a user returns and starts a new session, then that is a new conversation. Conversations do time out. I've only worked on enterprise engagements, so the time out varies. I believe default is 30 minutes, but that may change for Bluemix.
A better solution however is to have your application on determining it's time out, to dump the users profile variables to storage. When they return you can rebuild the relevant part of the conversation.
I am trying to create a custom paypal button for selling digital goods, that will direct the buyer to a link that will allow him to download the file.
I've read a bit this paypal article about advanced html variables but I am not sure which I have to use to make it work: https://developer.paypal.com/webapps/developer/docs/classic/paypal-payments-standard/integration-guide/Appx_websitestandard_htmlvariables/
Obviously the download should only initiate based on the payment ID to prevent free downloads, or is that done automatically by paypal?
What I would recommend us utilizing Instant Payment Notification (IPN) to handle all your post-payment processing tasks like updating your database, sending out email notifications (including one with a download link), etc.
Instant Payment Notification (IPN) is a message service that notifies
you of events related to PayPal transactions. You can use IPN messages
to automate back-office and administrative functions, such as
fulfilling orders, tracking customers, and providing status and other
transaction-related information.
This will allow you to not only automate the procedures, but also correctly handle things like e-checks or any other type of payment that may originally be in a "pending" status. You wouldn't want to deliver the digital goods until that payment actually clears. With IPN you will get 1 notification that your script can handle when the payment comes through as pending, and you would get another one when the payment updates to Completed, or Failed, or whatever.
The IPN's happen in real-time so buyers won't have to wait on anything. Whatever you're doing within the script would happen instantly upon the transaction completing.
I'm trying to learn about how to deal with the permissions/access requests in iOS 6. Everything I've found so far just kind of describes this vaguely without presenting any code samples etc. Are there any good resources/tutorials for this?
Specifically, I'm trying to discover whether there's a way to re-prompt the user programmatically to allow access to the address book etc. Or just general information on how to integrate this stuff into an app.
Under Address Book in the iOS 6 SDK Release Notes, it says:
Users are able to grant or deny access to contact data on a per-app basis. To request access to contact data, call the ABAddressBookRequestAccessWithCompletion function after calling the ABAddressBookCreateWithOptions function. The ABAddressBookRequestAccessWithCompletion function does not block the app while the user is being asked to grant or deny access. Until access has been granted, the ABAddressBookRef object will not contain any contacts, and any attempt to modify contacts fails with a kABOperationNotPermittedByUserError error. The user is prompted only the first time access is requested; any subsequent calls to ABAddressBookCreateWithOptions will use the existing permissions. The completion handler is called on an arbitrary queue. If the ABAddressBookRef object is used throughout the app, then all usage must be dispatched to the same queue to use ABAddressBookRef in a thread-safe manner.
Although this is only speaking for the Address Book, I'm sure it applies to Photos, Contacts, etc.
https://developer.apple.com/library/prerelease/ios/#releasenotes/General/RN-iOSSDK-6_0/_index.html#//apple_ref/doc/uid/TP40012166
What is the best practice to handle transaction between application and paypal.
Consider:
I'm Alice and I want send money to Bob
In my DB I see that Bob has $200 and I want to send him $150.
Once transaction is sent I want to update the Bob's account such that it would contain $50.
Now according to PayPal API I can send Pay and receive success. However what happens
if I for example send Pay it succeeds but I fail to receive a response due to network problem. So I assume that error happened and try again and technically I'll send $300 to Bob instead of $150?
How can I handle such a transaction - between a local database that keeps an account and the remote PayPal API?
I had this exact concern recently with an ASP.NET MVC project I was completing for a client.
I learned two things:
Communication between Paypal and your database cannot be trusted (well, didn't really learn this, but it was entirely reinforced)
I now understand why so many websites that have Paypal as a transaction type mention there could be a processing period between the time that the transaction was completed and shipping/delivery of the product is completed.
The way you handle the situation is similar to the way a business could handle personal checks:
A personal check looks like currency (and typically is), but many businesses would like some sort of verification from the bank that funds are available before they accept payment - so they use a machine that asks the bank if funds are actually available.
If the machine says the funds are available, the business trusts it and you complete the transaction. However, the machine can give an error message that typically means "the funds are not available or something went wrong" and the business has a decision to make:
We can trust the customer and accept the check, deliver the product, and hope for the best when later depositing the check to the bank.
Or we can tell the customer that it will take time for the check to clear, deposit the check, wait for the funds to actually arrive in our account, and (if successful) deliver the product after the business receives funding.
This sounds inefficient with the way many businesses operate today, but it is something that does come up. In fact, this is why a lot of businesses stray away from accepting personal checks, they are unreliable when compared to other methods of payment.
Now how does this correlate to handling a Paypal payment?
A Paypal payment looks like currency (and it typically is), but many businesses would like some sort of verification from the Paypal that funds are available before they accept payment - so they use Paypal PDT, IPN, or other method for checking that the transaction was handled appropriately.
If Paypal properly responds to one of the verification requests, the business can trust it and complete the transaction. However, your website may throw an error of some sort (i.e. Paypal could reply with an IPN response of NOTVALID, or you could never get a reply from Paypal). The business has a decision to make:
The business can trust the customer and accept that they have made a Paypal payment and everything should be alright (very bad decision in the case of a Paypal transaction)
Or the business can tell the customer at check-out time that there may be a 72 hour processing period for Paypal payments.
This may not sound like the best way to operate your business, but it is the way we have to deal with an imperfect internet.
I would set up the Paypal payment flow similar to this:
UserA wants to send $100 to another UserB using Paypal
UserA enters the value in the 'checkout field' and is sent over to Paypal to verify the transaction.
UserA is sent back to your website from Paypal and your website performs the IPN check with the details that Paypal has POSTed to your site(I chose IPN in this case - as if we were using Express Checkout as opposed to some other payment gateway that Paypal offers).
If the IPN is VALID, process the transaction as expected.
If the IPN is not VALID, mention to the customer that there may be a delay in processing, have your application send you a notification that a possible Paypal transaction issue has occurred (you may want to include a reference id so that you can quickly find which transaction this notification is referencing), and mark the transaction as pending as opposed to complete or something similar.
An admin of the site who handles these notifications will manually investigate the transaction (or force the website to check with Paypal again - see the Paypal API documentation for details on this) and manually mark the transaction as complete or failed.
Notify those involved of the status of the transaction.
It is annoying that we have to have extra steps involved to make sure the money was transferred, but, as mentioned earlier, we are using an imperfect system and we want to be very certain of the success / failure of financial transactions.
An added bonus to this process is that there is likely to be notifications when someone is tampering with the Paypal payment system - leaving you better equipped to deal with evil-doers in the future.
Please refer this link ,Hope PayPal Authorization & Capture method will be suitable for you ,since you don't want lose the response as well as miscalculated amount transfers, PayPal provides correlation id that can be referred for PayPal to confirm your order status,it will be better to pass the order id to PayPal API.
https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&content_ID=developer/howto_admin_authcapture
http://www.scribd.com/doc/6303345/40/CorrelationID-for-Reporting-Problems-to-PayPal
Good Luck!
This is known as 2-phase commit. As long as paypal does not participate in the same transaction, you will run into problems.
I would debit Alice the $150 and reflect the transaction is "Pending Confirmation", then periodically poll PayPal to synchronize your DB, since you have no control of when the network or PayPal may be available, post, reverse or adjust the transaction. Once PayPal processes the transaction, you can change the status in your DB from "Pending" to "Completed". BTW, this how bank accounts and credit cards are processed. You could apply a double-entry accounting method to your DB. (see this Q&A)
From what i see you need to make sure the transaction is complete otherwise nothing should be done .
If you deposit the money into PayPal API and you do not receive an response from PAYPAL API then you need to rollback the transaction in you DB.